1. Field of the Invention
The present invention relates generally to an optical cable used for transmission of an optical signal, and in particular, to an optical fiber composite ground wire (OPGW) using a steel tube, which functions as both a communication line and a ground wire.
2. Description of the Related Art
Electric lines are divided into an underground line and an aerial line. The aerial line is usually installed in areas other than cities for electric transmission. Due to probable lightening strikes on an electric line, an electric wire is installed as a lightning rod above the electric line. The electric wire is called a ground wire. The electric line, especially an electric transmission line needs a communication line for remote monitoring or remote control. The ground wire and the communication line are separately installed but it is preferable to integrate them.
However, a widely used conductor, such as copper or aluminum, is typically not suitable for the communication line because a nearby power line can generate an induced voltage or current and can thus cause a communication failure. The communication failure increases in proportion to the voltage and current strength of the power line and in inverse proportion to the distance between the communication line and the power line. In particular, an electric transmission line on which a high current flows at hundred thousands of volts, for example, can incur a serious communication failure on a nearby communication line. Nonetheless, a communication line should be provided to an electric transmission line. To overcome this problem, an optical fiber composite ground wire (OPGW) has been explored.
In this regard, an optical fiber composite ground wire (OPGW) using a steel tube exemplary of contemparory practice in the art includes acryl-coated optical fibers having an outer diameter of about 250 .mu.m, jelly on the circumference of the optical fibers, for protecting the optical fiber against water, a steel tube for inserting at least one optical fiber having the jelly, a central wire, inner layer wires surrounding the central wire and being aluminum-coated steel wires or aluminum wires, and outer layer wires surrounding the inner layer wires and being aluminum-coated steel wires or aluminum wires. In the optical fiber composite ground wire (OPGW) exemplary of contemparory practice in the art, the optical fibers are individually inserted into the steel tube and, thus, can be of different lengths due to application of different tensile forces on the optical fibers in a fabrication process, which can result in deterioration of optical transmission characteristics.
U.S. Pat. No. 4,078,853 to Kempf, et al. entiled Optical Communication Cable, disclose an optical communication cable including one or more cores of light-transmitting optical fibers substantially decoupled mechanically from the rest of the cable structure. It is disclosed each core can include linear arrays of optical fibers packaged in a plurality of ribbon structures which are stacked and hellically stranded for further strain-relief.
U.S. Pat. No. 4,359,598 to Dey, et al. entitled Overhaead Electric Transmission Systems, disclose a flexible stranded body, such as an electric conductor of an overhead electric transmission or distribution system, including at least one stranded layer of elongate elements of metal or metal alloy, at least one elongate compartment within and extending throughout the length of the stranded body and, loosely housed in the elongate compartment, at least one separate optical fibre and/or at least one optical bundle.
U.S. Pat. No. 4,491,386 to Negishi, et al. entitled Optical Fiber Cable And Process For Production Thereof, disclose an optical fiber cable including a linear center member having at least one longitudinal and spiral groove in the surface thereof, one coated optical fiber received in each groove, an outer sheath that encloses the center member, and a jelly-like material with which the space around each optical fiber is entirely filled.
U.S. Pat. No. 4,491,387 to Dey, et al. entitled Overhead Electric And Optical Transmission Systems, disclose a flexible stranded body, such as an electric conductor of an overhead electric transmission or distribution system, which includes at least one stranded layer of elongate elements of metal or metal alloy, at least one elongate compartment within and extending thoughout the length of the stranded body and, loosely housed on the elongate compartment, at least one separate optical fibre and/or at least one optical bundle.
U.S. Pat. No. 4,944,570 to Oglesby, et al. entitled Fiber Optic Cable Having An Extended Elongation Window, disclose a fiber optic cable including a central core which has one or more helical channels in its periphery. It is disclosed one or more tubes containing a dielectric water-blocking compound and one or more optical fibers are positioned in the channels. It is disclosed the fibers are randomly arranged within the tubes in such a way that tensile stresses on the cable are not transmitted to them, thus providing an elongation window. It is disclosed the assembly formed by the core and the tube or tubes is wrapped with a serving of metal wires.
U.S. Pat. No. 4,630,887 to Taylor entitled Optical Fiber Ribbon Structure, discloses an optical fibre ribbon structure suitable for use in an optical cable or other application where there is a risk that optical fibres will be subjected to a tensile force and includes a plurality of optical fibres and flexible reinforcing elements of resilient material arranged side by side and embedded in an elongate plastics body.
U.S. Pat. No. 4,666,244 to Van der Velde, et al. entitled Flat Type Optical Cable And An Optical Cable Composed Of Several Flat Type Cables, disclose a flat type optical cable including parallelly extending optical fibers which are interconnected by a light-cured lacquer of acrylic acid esters. It is disclosed the lacquer is present only on the facing circumferential parts of the optical fibers.
U.S. Pat. No. 4,775,213 to Kitayama entitled Composite Overhead Stranded Conductor Having A Filler Between Optical Fibers And A Protective Tube, disclose a composite stranded conductor bundle in which one of the cable strands is a fiber optic unit having a protective tube enclosing a plurality of optical fibers. It is disclosed the protective tube is filled with a fiber filler to hold the optical fibers.
U.S. Pat. No. 4,784,461 to Abe, et al. entitled Optical Cable With Improved Strength, disclose an optical cable having a central core with grooves along the outside, the grooves housing tubes containing optical fibers. It is disclosed the structure also allows for a different water blocking material to be used within the tubes than outside the tubes and within the grooves so as to satisfy different property requirements.
U.S. Pat. No. 4,793,686 to Saito entitled Optical Fiber Composite Overhead Transmission Line And Method For Producing Same, discloses an optical fiber composite overhead transmission line that includes a spacer formed with spiral grooves filled with a jelly-like material into which optical fibers are buried. It is disclosed a cover or sheath surrounds the spacer member to protect the internal components.
U.S. Pat. No. 4,865,415 to Kitayama entitled Composite Fiber-Optic Overhead ground wire, disclsoes a composite fiber-optic overhead ground wire having an optical unit which includes an optical fiber protecting tube, a spacer having helical grooves formed in its outer periphery, and multiple optical fiber units accommodated in the grooves of the spacer.
U.S. Pat. No. 5,195,158 to Bottoms, et al. entitled Tight Buffered Fiber Optic Groundwire Cable, disclose a fiber optic groundwire or static cable for use between spaced-apart support towers of an electrical power transmission network, for ground fault protection from lightning strikes and other electrical faults, with an integral fiber optic telecommunications bundle. It is disclosed a bundle of optical fibers tightly enclosed by a pliable thremally insulating strain jacket is firmly affixed into a helically-wound channel within an electrically conductive core, and at least one layer of stranded electrical conductors serving as strength members completely surrounds the core.
U.S. Pat. No. 5,204,926 to Bottoms, Jr., et al. entitled Tight Buffered Fiber Optic Groundwire Cable, disclose a fiber optic groundwire or static cable for use between spaced-apart support towers of an electric power transmission network, for ground fault protection from lightning strikes and other electrical faults, with an integral fiber optic telecommunications bundle. It is disclosed a bundle of optical fibers tightly enclosed by a pliable thermally insulating strain jacket is firmly affixed into a helically-wound channel within an electrically conductive core, and at least one layer of stranded electrical conductors serving as strength members completely surrounds the core. It is disclosed the wire can include at least one fiber optic subunit firmly affixed into a helically-wound channel within an electrically conductive core of the cable. It is disclosed the fiber optic subunit includes a plurality of optical fibers wound about a fiberglass central strength member having an overcoating layer of a pliable semicompressible material, and tightly enclosed by a pliable thermally insulating strain jacket.
U.S. Pat. No. 5,274,725 to Bottoms, et al. entitled Tight Buffered Fiber Optic Groundwire Cable, disclose a fiber optic groundwire or static cable for use between spaced-apart support towers of an electrical power transmission network, for ground fault protection from lightning strikes and other electrical faults, with an integral fiber optic telecommunications bundle. It is disclosed a bundle of optical fibers tightly enclosed by a pliable thermally insulating strain jacket is firmly affixed into a helically-wound channel within an electrically conductive core; and at least one layer of stranded electrical conductors serving as strength members completely surrounds the core. It is disclosed the wire can include at least one fiber optic subunit firmly affixed into a helically-wound channel within an electrically conductive core of the cable. It is disclosed the fiber optic subunit includes a plurality of optical fibers wound about a fiberglass central strength member having an overcoating layer of a pliable semicompressible material, and tightly enclosed by a pliable thermally insulating strain jacket.
U.S. Pat. No. 5,495,546 to Bottoms, et al. entitled Fiber Optic Groundwire With Coated Fiber Enclosures, disclose an optic static wire assembly including a central core which has one or more helical channels in its periphery. It is disclosed one or more tubes containing a dielectric water-blocking compound and one or more optical fibers are positioned in the channels. It is disclosed the tubes are coated with a thermal insulation material, and then a heat reflective material. It is disclosed the optical fibers are randomly arranged within the tubes in such a way that tensile stresses on the cable are not transmitted to them. It is disclosed the assembly formed by the core and the tube or tubes is wrapped with a serving of metal wires.
U.S. Pat. No. 5,524,164 to Hattori, et al. entitled Coated Tape Form Optical Fiber Wire, disclose a tape form optical fiber wire including at least one set of at least two optical fibers each of which has a protective coating layer and which are arranged in parallel in the same plane, at least one set of the optical fibers being integrated by at least one common coating layer, in which the common coating layer contains a main component of a common coating resin and a component having a poor compatibility with the main component.
U.S. Pat. No. 5,787,217 to Traut, et al. entitled Fiber Optic Ground Wire Cable, disclose a fiber optic cable core structure that includes a plurality of fiber optic mini-bundles, each of which includes a plurality of optical fibers bonded together in a first curable material. It is disclosed the fiber optic mini-bundles in turn are bonded together as a unitary structure by a second curable material, and the resulting structure is wrapped in a metal tube-like ring.
U.S. Pat. Reissue No. RE032,374 to Dey, et al. entitled Overhead Electric And Optical Transmission Cables, disclose a flexible stranded body, such as an electic conductor of an overhead electric transmission or distribution system, including at least one stranded layer of elongate elements of metal or metal alloy, at least one elongate compartment within and extending throughout the length of the stranded body and, loosely housed in the elongate compartment, at least one separate optical fibre and/or at least one optical bundle.